CA2266682C - Manufacture of planar waveguide and planar waveguide - Google Patents
Manufacture of planar waveguide and planar waveguide Download PDFInfo
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- CA2266682C CA2266682C CA002266682A CA2266682A CA2266682C CA 2266682 C CA2266682 C CA 2266682C CA 002266682 A CA002266682 A CA 002266682A CA 2266682 A CA2266682 A CA 2266682A CA 2266682 C CA2266682 C CA 2266682C
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- electrodes
- core area
- planar waveguide
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- substrate
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/355—Non-linear optics characterised by the materials used
- G02F1/3558—Poled materials, e.g. with periodic poling; Fabrication of domain inverted structures, e.g. for quasi-phase-matching [QPM]
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/13—Integrated optical circuits characterised by the manufacturing method
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12083—Constructional arrangements
- G02B2006/12107—Grating
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- Physics & Mathematics (AREA)
- Nonlinear Science (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Optical Integrated Circuits (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
Abstract
A metal film (12) is formed on the surface of a glass substrate (10) and etched to form a pair of electrodes (12a and 12b) which face each other with a certain gap therebetween (S11-S13). The substrate (10) is doped with germanium, etc, by using the electrodes (12a and 12b) as a mask to form a co re part (14, S14). Then a high voltage is applied between the electrodes while ultraviolet radiation is applied and the core part (14) is subjected to ultraviolet-driven boring to give the optical nonlinearity to the core part (14, S15). The voltage application to the core part (14) having the optical nonlinearity is controlled to control a light transmitting through the core part (14).
Description
SPECIFICATION
MANUFACTURE OF PLANAR WAVEGUIDE AND PLANAR WAVEGUIDE
[FIELD OF THE INVENTION]
The present invention relates to a planar waveguide having optical nonlinearity and particularly to one which makes use of ultraviolet excitation poling.
[BACKGROUND OF THE INVENTION]
With recent advances in information processing technology involving computers and the like , the need and desire to process and transmit massive amounts of data (mass-data) at high speeds have increased. Currently, opticalfiber transmission isthemost effective means for mass-information transmission and has become widely used.
optical fiber transmission works by transmitting optical signals through optical fiber. In order to transmit signals through optical fiber, elements such as a light source, a light receiving element, an optical signal generator, an optical switch/coupler, transmission optical fiber, and the like are necessary. An electrooptical effect (optical nonlinearity, a phenomenon which results from nonlinear polarization generated in a substanceby light) isthenusedforanopticalfunctionalelement suchasanopticalsignalgenerator, anopticalswitchandthe like.
Therefore, an optical switch element and the like are produced by controllingelectricfieldstrengthappliedtoanopticalnonlinear materialtochangeintensityordirectionoflighttransmittedinto the optical nonlinear material.
.. . . .. . .
Optical fiber transmission of information can be achieved by applying optical modulation to light introduced into the optical fiber on the basis of information to be transmitted by making use of an optical functional element and then demodulating the light signal on the light-receiving side.
Crystalline materials such as LiNbO3, BaTiO3 and the like are now commonly used as an optical nonlinear material because there are, at present, no other materials that can realize sufficient nonlinearity.
On the other hand, from the standpoint of stable connection with glass-made optical fiber, low losses in transmitted light, reduction of cost, wide range of transmitted wavelength and the like, it is preferable to construct an optical functional element such as an optical switch or the like from a glass material.
Accordingly, attempts have been made to impart optical nonlinearity in glass materials. For example, ultraviolet excitation poling by irradiating a glass materialwithultraviolet light in a state where high electric field of approximately 10 6 V/cm is applied is described in "ELECTRONICS LETTERS 30th March 1995 Vol.31 No.7 pp.573-574" .
It is believed that ultraviolet excitation poling is able to impart to a glass material optical nonlinearity equal to that of a crystalline material , which may then be preferably used as an optical functional element.
Although according to the conventionally proposed ultraviolet excitation poling described above, nonlinearity may be given to the glass materials, that nonlinearity is given only to a definite area of the core of the optical fiber. Therefore, only the possibility of availability for an optical functional element is shown.
Further , although an optical fiber optical functional element has additional advantages such as simple connection for transmission, functions are limited and shape dependent.On the other hand, a planar waveguide is also able to form plural waveguides, and a diversification of processing function may be attempted. It is considered that if optical nonlinearity may be given to the glass-made substrate, a planar waveguide preferable for various applications can be obtained.
[DESCRIPTION OF THE INVENTION]
The present invention has been achieved in light of the aforementioned problems and its objective is to present a process for producing a planar waveguide by giving optical nonlinearity to a glass-made substrate to realize a planar waveguide having optical nonlinearity.
The process for producing a planar waveguide according to the present invention is characterized in that a pair of electrodes of conducting material is arranged at a gap corresponding to core area of waveguide on the surface of the glass-made substrate and the surface of the glass-made substrate is irradiated with ultraviolet light through said gap in a state where voltage is applied between these electrodes so that ultraviolet excitation poling is applied to the core area.
According to the present invention as outlined above, an opticalnonlinearity is introduced to thecoreareaofthe surface of the glass substrate by applying the ultraviolet excitation poling thereto. Therefore, a variety of functionscan be effected by controlling the electric field applied to the core area having the optical nonlinearity. Further, since the nonlinearity can be given to only a part of the glass substrate, such effects as low cost, easiness of connection with glass-made optical fiber and the like can be obtained. Particularly, since the nonlinearity coefficient more than several P m/V similarly to that of LiNbO3 can be obtained according to the ultraviolet excitation poling to the glass, and its response to electric field becomes sufficient for application.
The present invention is also characterized in that a step for forming a conducting metal film on the surface of the glass substrate, a step for etching the metal film thus formed to form a pair of electrodes at a determined gap, a step for introducing specified atoms in the surface of the substrate under the aforementioned gap using the electrodes thus formed as masks to form core area, and a step for irradiating the core area with ultraviolet light in a state where voltage is applied between the pair of electrodes to effect ultraviolet excitation poling are completed to give optical nonlinearity to the core area.
As described above, by forming the core area after the metal film is etched, the core area can be formed under the gap between theelectrodes, andtheultraviolet excitation polingcan beeasily and certainly applied to desired area of optical waveguide.
The present invention is further characterized in that the irradiation withultraviolet light to the aforementionedcore area is carried out through a given phase mask, and parts having optical nonlinearity are formed periodically in the core area.
As described above, gratings can be formed in the core area by discontinuous irradiation with ultraviolet light. Light of a specified wavelength (Bragg wavelength) can then be reflected and interfered by these gratings. As the Bragg wavelength varies according to applied voltage, it is possible to make the core area operate as, for example, a wavelength switch.
In particular, according to the present invention, the gratings can be easily formed using a simple process of limiting the area to be irradiated with ultraviolet light using a phase mask.
The planar waveguide of the present invention can also be characterized by its inclusion of a glass substrate, a pair of electrodes formed on the substratethrough a determined gap, acore area which is formed on the surface of the substrate under the gap between the pair of electrodes and the refractive index of which is different from that of the substrate by addition of specified atoms, and the aforementioned core area being given optical nonlinearityof lpm/Voraboveastheelectro-opticalcoefficient.
[BRIEF DESCRIPTION OF THE DRAWINGS]
Fig.1 is a view illustrating the structure of a planar waveguide of a working embodiment of the present invention.
Fig.2 is a view illustrating the steps for producing a planar waveguide.
Fig.3 is a view illustrating the structure of a planar waveguide having gratings.
Fig.4 is a view illustrating the structure of a phase mask.
Fig.5 is a view illustrating an example of an optical functional element.
Fig.6 is a view illustrating an example of an optical functional element.
Fig.7 isaviewillustratinganexampleofstructureofsystem.
[PREFERRED EMBODIMENT FOR WORKING THE PRESENT INVENTION]
The preferred embodiment for working the present invention (herinafter referred to as the working embodiment) will be described below with reference to the appended drawings.
Fig.1 is a schematic view illustrating the structure of a planar waveguide of the present invention. A glass substrate 10 is made of silica glass (SiO2) in the form of a plate and a pair of electrodes 12a and 12b are formed on its surface. These electrodes 12a and 12b may be made of, for example, a thin film of aluminum (Al). Core area 14, doped with germanium (Ge) or a similar material with an adjusted refractive index, is formed under the gap between the pair of electrodes 12a and 12b.
optical nonlinearity is then introduced to the core area 14 by means of ultraviolet excitation poling, thereafter making it possible to control the optical properties of the core area 14 using a voltage applied between the electrodes 12a and 12b.
Accordingly, the lightpassing into thecorearea 14 iscontrolled byvoltageappliedbetweentheelectrodes12a and 12band theplanar waveguide operates as an optical functional element.
[PROCESS FOR PRODUCTION]
Fig.2 outlines a process for production of such a planar waveguide. First, a substrate 10 made of a silica glass plate is .
prepared (S11). Then, a metal film 12 is formed on the surface of the substrate 10 (S12). This is carried out, for example, by placing the glass substrate 10 in a vacuum chamber and depositing a metal on the surface of the glass substrate 10. This metal to be deposited may be, for example, aluminum. Methods other than deposition may also be used to form the metal film 12.
Next, a determined portion of the metal film 12 is removed by etching, thereby forming two electrodes 12a and 12b (S13). In this example, a straight gap is formed between both electrodes 12a and 12b and etching is carried out by means of photolithography, etc. That is to say, a resist is formed by deposition over the entire surface of the metal film 12, and then the resist is irradiated with light through a mask pattern to expose only the desired area of the resist.
Next, doping of GeO2(germanium oxide) is carried out using the electrodes 12a and 12b as a mask (S14). By this doping of germanium oxide the, core area 14, which operates as a waveguide with a refractive index different from the surrounding areas, is formed in the doped area. In such a manner as described above, the core area can be accurately formed in the area between the electrodes and ultraviolet excitation poling can be accurately performed on the core area. The core area may, of course, be easily be formed in any suitable shape, while the positions of the electrodes will of necessity correspond to the core area.
When an element having an unrestricted waveguide is formed, germanium oxide or the like are added to the whole of the glass substrate 10, and its refractive index is adjusted. Doping step S14 is therefore omitted. In this example, the gap is established --by approximately 10~m.
Asdescribedabove,whentheelectrodes12aand12bareformed, irradiation with ultraviolet light is carried out in a state where a determined high voltage is applied between the electrodes 12a and12b, andtheultravioletexcitationpolingtreatment isapplied to the core area 14 (S15).
That is to say, a voltage of about 1 kV is applied between the electrodes 12a and 12b. An electric field of about 106V/cm is nowappliedtothecorearea 14. Inthisstate, apulsedArFexcimer laser (wavelength 193nm) is used to irradiate the core area 14 with ultraviolet light. The energy density, repetitive interval of pulse and irradiation time of this laser are about 36mJ/cm2, about 10pps (pulse /second) and about 10 to about 30 minutes, respectively.
However, there is a danger of discharge in an area facing to the gap between the electrodes 12a and 12b. It is, therefore, preferabletocarryout theultraviolet excitationpoling invacuo.
In this way, discharge between the electrodes 12a and 12b can be prevented and effective ultraviolet excitation poling can be achieved.
In the manner described above, optical nonlinearity can be given to the core area 14. That is to say, with the above ultraviolet excitation poling treatment, a primary electrooptical coefficient (r) ofapproximately 6pm/Vcanbe obtained in thecore area. ThiS is a value comparable to that of LiNbO3 and the like, and is sufficient for the formation of an optical functional element.
The electrodes 12a and 12b which were used in order to apply voltage at the time of ultraviolet excitation poling in the planar waveguide remain on the substrateandcan beusedto apply adesired electric field to the core area 14. It is thereafter a simple process to impart and operate any combination of a variety of functions.
While the ultraviolet excitation poling was applied to only one place in the present illustrative example, it may also be preferable that the electrodes 12a and 12b be independently formed at preferable locations on the glass substrate 10, and that an elemental region having optical nonlinearity be formed on each place on the glass substrate 10.
[MODIFICATION]
It may also be preferable to configure the present invention by forming alternate and periodic regions having optical nonlinearity and usual regions on the core area 14, and to use these as grating sections. That is to say, as shown in Fig.3, the nonlinear regions 16a having a different refractive index and secondarynonlinearityare formedonthecorearea14perpindicular to the lengthwise direction at predetermined intervals and with specified width to form the grating section 16 along with the usual regions 16b. Therefore, light which is transmitted through the corearea14initslengthwisedirectionisreflectedandinterfered by the grating section 16.
Therefractiveindexofthenonlinearregion16acanbealtered by controlling the voltage applied between the electrodes 12a and 12b. Thewavelengthofreflectedand interfered lightthenbecomes different, and the wavelength of the light which intercepts the transmission can then be controlled by applied voltage and this modification can beutilized as a wavelength switchor a wavelength selection element.
A planar waveguide as described above may be formed in such a manner as will be describe below. That is to say, optical fibers are irradiated with ultraviolet light laser through a phase mask at the time of the aforementioned ultraviolet excitation poling.
One example of the structure of the phase mask is illustrated in Fig. 4. As shown in Fig. 4, a plurality of grooves 22 are formed on the surface of one side of the plate substrate 20. The grooves 22 are formed in parallel with each other and at predetermined spacings. Accordingly, a predetermined diffraction phenomenon occurswhen parallellight istransmittedthroughthegrooves,with high and low intensities of the light being repeated at predetermined spacings. That is to say, fringe patterns (zebra patterns) are formed, in which light-irradiated regions and non-light-irradiatedregionsareperiodicallyrepeated. Further, desired places can be irradiated with desired ultraviolet light byusinga pluralityofphasemasks. The substrate20Ofthe phase maskmay,forexample,bemadeofsilicaglass(SiO2)whichtransmits ultraviolet light.
Accordingly, the optical nonlinearity can be given only to the places irradiated with ultraviolet light and such the planar waveguide as shown in Fig.3 can be formed.
And, when a voltage, particularly negative voltage (several hundred V, approximately) is applied to such a planar waveguide in a state where light of various wavelengths isconducted thereto, the wavelength intercepted by such a waveguide shifts. Therefore, this waveguide may be utilized as a wavelength switch. With respect to positive and negative of voltage, the electric field opposite to poling electric field may be taken as positive.
As mentioned above, the transmission strength of light of 6 the specific wavelength decreases at the grating element because Bragg reflection occurs in the grating and light of the Bragg wavelength is reflected.
Further, theBraggwavelengthshifts whenavoltageisapplied and the Bragg reflection increases or decreases according to the applied voltage because the core area 14 at the region irradiated with ultraviolet light comes to have the nonlinearity by the ultraviolet excitation poling and the primary electrooptical effect occurs and the effective reflective index of the waveguide changes.
Variation in refractive index by the electrooptical effect (AnEO) can represented by the following equation;
~nEO=-n3rE/2. In this equation, n is the refractive index of the core area of fiber, r is the primary electrooptical effect coefficient and E is electric field strength.
Bragg wavelength (A2) is then represented by A2=Aneff wherein A is a pitch of the grating. And, in the consideration on the basis of coupling of forward and backward (reflection) guided light, the peak reflectance (R) isrepresented by R=tan h2 ( K L), and 3dB band width (A A ) is represented by AA=A2 {~r2+ ( /cL) 2} ~-S/2n~,~f L
wherein~Kisthe couplingcoefficient offorward and backward (reflection) guided light, and is represented by ~=~nC~n~ /A3 n~ff . Wherein L is length of the grating element.
AlSo, n~ff iS effective refractive index of guided light at the grating section, nc is the refractive index of cladding,~n is the magnitude of change in the refractive index forming periodic structure, and ~is overlapping integral in forward and backward transmission modes.
Therefore, neff ~n and ~ change depending upon ~nEO.
The relationship between the variation in the effective refractive index (~nEO) and the applied voltage was studied experimentally from the relationship between the changes in the voltage applied and the changes in the Bragg wavelength. As the result, the effective refractive index (n~ff) has a determined negative slope to the changes in the voltage applied and changes linearly. Thatistosay,theeffectiverefractiveindexdecreases depending upon an application of voltage and the Bragg wavelength shifts to the side of short wavelength.
And, in such the planar waveguide as described above, the changes in the Bragg wavelength (A A3) to electric field (lV/
~m) is approximately 0.01 nm.
As described above, there is a linear relationship between the applied voltage and the effective refractive index and it is understood that the Pockels effect (the primary electrooptical effect) on the basis of the secondary optical nonlinearity is obtained.
It is, therefore, possible to switch light of a specific wavelength by shifting the Bragg wavelength by an application of voltage to control the transmission and non-transmission of laser light. Particularly, the planar waveguide of the present working embodiment is made of glass. Therefore, the connection with conventional optical fiber may be easily carried out. That is to say, theconnection by adhesive, laser fusing, melt-connection and the like can be easily carried out. Further, the transmittance of light at the element may be sufficiently maintained and mode mismatch is prevented .
Stillfurther, theBraggwavelength maybeshiftedinmultiple stepsby successivelychanging voltage applied. Thereby, thismay be also utilized as a wavelength selection element by controlling the transmitted wavelength.
Furthermore, in the present embodiment, the spacings of the grating may be easily controlled by the phase mask. Therefore, the grating element having desired Bragg wavelength may be easily obtained.
[ ANOTHER STRUCTURE ]
The planar waveguide of the present invention may be utilized in a variety of functional elements. For example, it may be preferable as shown in Fig. 5 to design a structure where the core area 14 is once divided to two branches which rejoin each other, and the electrodes 12a and 12b are placed respectively to the branched portions so as to apply voltage.
With such a structure, it is possible to control the phases of two branched two light rays by controlling the voltage applied tothetwobranchedportions, andit isthereforepossibletoeffect the attenuation of output light by shifting the phases of both 180 degree and optical strength modulation.
Arrangementofelectrodesisnotrestrictedtothearrangement shown in Fig.5,and electrodes 12c and 12d may also be placed on the core area 14 as shown in Fig.6. In this case, the electrodes 12cand 12dmay bepreferablyformed afterremovaloftheelectrodes 12a and 12b which have been used at the time of ultraviolet light poling. With such the structure, modulation similar to that described above may be effected.
According to the planar waveguide of the present invention, portions having optical nonlinearity may be formed on any desired area of the glass substrate 10. Therefore, various kinds of optical functional elements and optical functional circuits may be formed.
For example, a signal generator, an optical switch/coupler, or the like for the two-way optical transmission system shown in Fig.7 may be configured using the planar waveguide of the present invention. Thatistosay,twoterminalslOOareshowninthesystem illustrated in Fig.7 (there are a number of terminals 100 in conventional systems). These terminals 100 are connected with optical fiber 102 via a transducer 104. The transducer 104 controls the connection of desired optical fiber 102.
Each terminal 100 comprises a light source lOOa, a signal generator lOOb, an optical switch/coupler, and a light receiving element lOOd. The light source lOOa is a laser source generating a specific light,andthesignalgeneratorlOObopticallymodulates that light to include the information to be transmitted. The optical switch/coupler lOOc transmits the optical signals generated from the signal generator lOOb to the transmission optical fiber 102 at the time of transmission and supplies the optical signals generated from the transmission optical fiber 102 to the light receiving element lOOd at the time of receiving. The light receiving element lOOd transduces input optical signals to electric signals. The information transmitted may be demodulated by modulating the electric signals obtained by the light receiving element lOOd. An optical connector 106 connects the terminal 100 with the transmission optical fiber 102.
As described above, a transmission system making use of opticalfibermaybemadeup,andtheplanarwaveguideofthepresent inventionmaybepreferablyutilizedwiththesignalgeneratorlOOb, the optical switch/coupler lOOc, or the like.
[INDUSTRIAL APPLICABILITY]
The present invention may be utilized for an optical 16 functional element such as an optical signal generator, an optical switch/coupler, or any similar element in an optical fiber transmission system.
.. . . . ..
MANUFACTURE OF PLANAR WAVEGUIDE AND PLANAR WAVEGUIDE
[FIELD OF THE INVENTION]
The present invention relates to a planar waveguide having optical nonlinearity and particularly to one which makes use of ultraviolet excitation poling.
[BACKGROUND OF THE INVENTION]
With recent advances in information processing technology involving computers and the like , the need and desire to process and transmit massive amounts of data (mass-data) at high speeds have increased. Currently, opticalfiber transmission isthemost effective means for mass-information transmission and has become widely used.
optical fiber transmission works by transmitting optical signals through optical fiber. In order to transmit signals through optical fiber, elements such as a light source, a light receiving element, an optical signal generator, an optical switch/coupler, transmission optical fiber, and the like are necessary. An electrooptical effect (optical nonlinearity, a phenomenon which results from nonlinear polarization generated in a substanceby light) isthenusedforanopticalfunctionalelement suchasanopticalsignalgenerator, anopticalswitchandthe like.
Therefore, an optical switch element and the like are produced by controllingelectricfieldstrengthappliedtoanopticalnonlinear materialtochangeintensityordirectionoflighttransmittedinto the optical nonlinear material.
.. . . .. . .
Optical fiber transmission of information can be achieved by applying optical modulation to light introduced into the optical fiber on the basis of information to be transmitted by making use of an optical functional element and then demodulating the light signal on the light-receiving side.
Crystalline materials such as LiNbO3, BaTiO3 and the like are now commonly used as an optical nonlinear material because there are, at present, no other materials that can realize sufficient nonlinearity.
On the other hand, from the standpoint of stable connection with glass-made optical fiber, low losses in transmitted light, reduction of cost, wide range of transmitted wavelength and the like, it is preferable to construct an optical functional element such as an optical switch or the like from a glass material.
Accordingly, attempts have been made to impart optical nonlinearity in glass materials. For example, ultraviolet excitation poling by irradiating a glass materialwithultraviolet light in a state where high electric field of approximately 10 6 V/cm is applied is described in "ELECTRONICS LETTERS 30th March 1995 Vol.31 No.7 pp.573-574" .
It is believed that ultraviolet excitation poling is able to impart to a glass material optical nonlinearity equal to that of a crystalline material , which may then be preferably used as an optical functional element.
Although according to the conventionally proposed ultraviolet excitation poling described above, nonlinearity may be given to the glass materials, that nonlinearity is given only to a definite area of the core of the optical fiber. Therefore, only the possibility of availability for an optical functional element is shown.
Further , although an optical fiber optical functional element has additional advantages such as simple connection for transmission, functions are limited and shape dependent.On the other hand, a planar waveguide is also able to form plural waveguides, and a diversification of processing function may be attempted. It is considered that if optical nonlinearity may be given to the glass-made substrate, a planar waveguide preferable for various applications can be obtained.
[DESCRIPTION OF THE INVENTION]
The present invention has been achieved in light of the aforementioned problems and its objective is to present a process for producing a planar waveguide by giving optical nonlinearity to a glass-made substrate to realize a planar waveguide having optical nonlinearity.
The process for producing a planar waveguide according to the present invention is characterized in that a pair of electrodes of conducting material is arranged at a gap corresponding to core area of waveguide on the surface of the glass-made substrate and the surface of the glass-made substrate is irradiated with ultraviolet light through said gap in a state where voltage is applied between these electrodes so that ultraviolet excitation poling is applied to the core area.
According to the present invention as outlined above, an opticalnonlinearity is introduced to thecoreareaofthe surface of the glass substrate by applying the ultraviolet excitation poling thereto. Therefore, a variety of functionscan be effected by controlling the electric field applied to the core area having the optical nonlinearity. Further, since the nonlinearity can be given to only a part of the glass substrate, such effects as low cost, easiness of connection with glass-made optical fiber and the like can be obtained. Particularly, since the nonlinearity coefficient more than several P m/V similarly to that of LiNbO3 can be obtained according to the ultraviolet excitation poling to the glass, and its response to electric field becomes sufficient for application.
The present invention is also characterized in that a step for forming a conducting metal film on the surface of the glass substrate, a step for etching the metal film thus formed to form a pair of electrodes at a determined gap, a step for introducing specified atoms in the surface of the substrate under the aforementioned gap using the electrodes thus formed as masks to form core area, and a step for irradiating the core area with ultraviolet light in a state where voltage is applied between the pair of electrodes to effect ultraviolet excitation poling are completed to give optical nonlinearity to the core area.
As described above, by forming the core area after the metal film is etched, the core area can be formed under the gap between theelectrodes, andtheultraviolet excitation polingcan beeasily and certainly applied to desired area of optical waveguide.
The present invention is further characterized in that the irradiation withultraviolet light to the aforementionedcore area is carried out through a given phase mask, and parts having optical nonlinearity are formed periodically in the core area.
As described above, gratings can be formed in the core area by discontinuous irradiation with ultraviolet light. Light of a specified wavelength (Bragg wavelength) can then be reflected and interfered by these gratings. As the Bragg wavelength varies according to applied voltage, it is possible to make the core area operate as, for example, a wavelength switch.
In particular, according to the present invention, the gratings can be easily formed using a simple process of limiting the area to be irradiated with ultraviolet light using a phase mask.
The planar waveguide of the present invention can also be characterized by its inclusion of a glass substrate, a pair of electrodes formed on the substratethrough a determined gap, acore area which is formed on the surface of the substrate under the gap between the pair of electrodes and the refractive index of which is different from that of the substrate by addition of specified atoms, and the aforementioned core area being given optical nonlinearityof lpm/Voraboveastheelectro-opticalcoefficient.
[BRIEF DESCRIPTION OF THE DRAWINGS]
Fig.1 is a view illustrating the structure of a planar waveguide of a working embodiment of the present invention.
Fig.2 is a view illustrating the steps for producing a planar waveguide.
Fig.3 is a view illustrating the structure of a planar waveguide having gratings.
Fig.4 is a view illustrating the structure of a phase mask.
Fig.5 is a view illustrating an example of an optical functional element.
Fig.6 is a view illustrating an example of an optical functional element.
Fig.7 isaviewillustratinganexampleofstructureofsystem.
[PREFERRED EMBODIMENT FOR WORKING THE PRESENT INVENTION]
The preferred embodiment for working the present invention (herinafter referred to as the working embodiment) will be described below with reference to the appended drawings.
Fig.1 is a schematic view illustrating the structure of a planar waveguide of the present invention. A glass substrate 10 is made of silica glass (SiO2) in the form of a plate and a pair of electrodes 12a and 12b are formed on its surface. These electrodes 12a and 12b may be made of, for example, a thin film of aluminum (Al). Core area 14, doped with germanium (Ge) or a similar material with an adjusted refractive index, is formed under the gap between the pair of electrodes 12a and 12b.
optical nonlinearity is then introduced to the core area 14 by means of ultraviolet excitation poling, thereafter making it possible to control the optical properties of the core area 14 using a voltage applied between the electrodes 12a and 12b.
Accordingly, the lightpassing into thecorearea 14 iscontrolled byvoltageappliedbetweentheelectrodes12a and 12band theplanar waveguide operates as an optical functional element.
[PROCESS FOR PRODUCTION]
Fig.2 outlines a process for production of such a planar waveguide. First, a substrate 10 made of a silica glass plate is .
prepared (S11). Then, a metal film 12 is formed on the surface of the substrate 10 (S12). This is carried out, for example, by placing the glass substrate 10 in a vacuum chamber and depositing a metal on the surface of the glass substrate 10. This metal to be deposited may be, for example, aluminum. Methods other than deposition may also be used to form the metal film 12.
Next, a determined portion of the metal film 12 is removed by etching, thereby forming two electrodes 12a and 12b (S13). In this example, a straight gap is formed between both electrodes 12a and 12b and etching is carried out by means of photolithography, etc. That is to say, a resist is formed by deposition over the entire surface of the metal film 12, and then the resist is irradiated with light through a mask pattern to expose only the desired area of the resist.
Next, doping of GeO2(germanium oxide) is carried out using the electrodes 12a and 12b as a mask (S14). By this doping of germanium oxide the, core area 14, which operates as a waveguide with a refractive index different from the surrounding areas, is formed in the doped area. In such a manner as described above, the core area can be accurately formed in the area between the electrodes and ultraviolet excitation poling can be accurately performed on the core area. The core area may, of course, be easily be formed in any suitable shape, while the positions of the electrodes will of necessity correspond to the core area.
When an element having an unrestricted waveguide is formed, germanium oxide or the like are added to the whole of the glass substrate 10, and its refractive index is adjusted. Doping step S14 is therefore omitted. In this example, the gap is established --by approximately 10~m.
Asdescribedabove,whentheelectrodes12aand12bareformed, irradiation with ultraviolet light is carried out in a state where a determined high voltage is applied between the electrodes 12a and12b, andtheultravioletexcitationpolingtreatment isapplied to the core area 14 (S15).
That is to say, a voltage of about 1 kV is applied between the electrodes 12a and 12b. An electric field of about 106V/cm is nowappliedtothecorearea 14. Inthisstate, apulsedArFexcimer laser (wavelength 193nm) is used to irradiate the core area 14 with ultraviolet light. The energy density, repetitive interval of pulse and irradiation time of this laser are about 36mJ/cm2, about 10pps (pulse /second) and about 10 to about 30 minutes, respectively.
However, there is a danger of discharge in an area facing to the gap between the electrodes 12a and 12b. It is, therefore, preferabletocarryout theultraviolet excitationpoling invacuo.
In this way, discharge between the electrodes 12a and 12b can be prevented and effective ultraviolet excitation poling can be achieved.
In the manner described above, optical nonlinearity can be given to the core area 14. That is to say, with the above ultraviolet excitation poling treatment, a primary electrooptical coefficient (r) ofapproximately 6pm/Vcanbe obtained in thecore area. ThiS is a value comparable to that of LiNbO3 and the like, and is sufficient for the formation of an optical functional element.
The electrodes 12a and 12b which were used in order to apply voltage at the time of ultraviolet excitation poling in the planar waveguide remain on the substrateandcan beusedto apply adesired electric field to the core area 14. It is thereafter a simple process to impart and operate any combination of a variety of functions.
While the ultraviolet excitation poling was applied to only one place in the present illustrative example, it may also be preferable that the electrodes 12a and 12b be independently formed at preferable locations on the glass substrate 10, and that an elemental region having optical nonlinearity be formed on each place on the glass substrate 10.
[MODIFICATION]
It may also be preferable to configure the present invention by forming alternate and periodic regions having optical nonlinearity and usual regions on the core area 14, and to use these as grating sections. That is to say, as shown in Fig.3, the nonlinear regions 16a having a different refractive index and secondarynonlinearityare formedonthecorearea14perpindicular to the lengthwise direction at predetermined intervals and with specified width to form the grating section 16 along with the usual regions 16b. Therefore, light which is transmitted through the corearea14initslengthwisedirectionisreflectedandinterfered by the grating section 16.
Therefractiveindexofthenonlinearregion16acanbealtered by controlling the voltage applied between the electrodes 12a and 12b. Thewavelengthofreflectedand interfered lightthenbecomes different, and the wavelength of the light which intercepts the transmission can then be controlled by applied voltage and this modification can beutilized as a wavelength switchor a wavelength selection element.
A planar waveguide as described above may be formed in such a manner as will be describe below. That is to say, optical fibers are irradiated with ultraviolet light laser through a phase mask at the time of the aforementioned ultraviolet excitation poling.
One example of the structure of the phase mask is illustrated in Fig. 4. As shown in Fig. 4, a plurality of grooves 22 are formed on the surface of one side of the plate substrate 20. The grooves 22 are formed in parallel with each other and at predetermined spacings. Accordingly, a predetermined diffraction phenomenon occurswhen parallellight istransmittedthroughthegrooves,with high and low intensities of the light being repeated at predetermined spacings. That is to say, fringe patterns (zebra patterns) are formed, in which light-irradiated regions and non-light-irradiatedregionsareperiodicallyrepeated. Further, desired places can be irradiated with desired ultraviolet light byusinga pluralityofphasemasks. The substrate20Ofthe phase maskmay,forexample,bemadeofsilicaglass(SiO2)whichtransmits ultraviolet light.
Accordingly, the optical nonlinearity can be given only to the places irradiated with ultraviolet light and such the planar waveguide as shown in Fig.3 can be formed.
And, when a voltage, particularly negative voltage (several hundred V, approximately) is applied to such a planar waveguide in a state where light of various wavelengths isconducted thereto, the wavelength intercepted by such a waveguide shifts. Therefore, this waveguide may be utilized as a wavelength switch. With respect to positive and negative of voltage, the electric field opposite to poling electric field may be taken as positive.
As mentioned above, the transmission strength of light of 6 the specific wavelength decreases at the grating element because Bragg reflection occurs in the grating and light of the Bragg wavelength is reflected.
Further, theBraggwavelengthshifts whenavoltageisapplied and the Bragg reflection increases or decreases according to the applied voltage because the core area 14 at the region irradiated with ultraviolet light comes to have the nonlinearity by the ultraviolet excitation poling and the primary electrooptical effect occurs and the effective reflective index of the waveguide changes.
Variation in refractive index by the electrooptical effect (AnEO) can represented by the following equation;
~nEO=-n3rE/2. In this equation, n is the refractive index of the core area of fiber, r is the primary electrooptical effect coefficient and E is electric field strength.
Bragg wavelength (A2) is then represented by A2=Aneff wherein A is a pitch of the grating. And, in the consideration on the basis of coupling of forward and backward (reflection) guided light, the peak reflectance (R) isrepresented by R=tan h2 ( K L), and 3dB band width (A A ) is represented by AA=A2 {~r2+ ( /cL) 2} ~-S/2n~,~f L
wherein~Kisthe couplingcoefficient offorward and backward (reflection) guided light, and is represented by ~=~nC~n~ /A3 n~ff . Wherein L is length of the grating element.
AlSo, n~ff iS effective refractive index of guided light at the grating section, nc is the refractive index of cladding,~n is the magnitude of change in the refractive index forming periodic structure, and ~is overlapping integral in forward and backward transmission modes.
Therefore, neff ~n and ~ change depending upon ~nEO.
The relationship between the variation in the effective refractive index (~nEO) and the applied voltage was studied experimentally from the relationship between the changes in the voltage applied and the changes in the Bragg wavelength. As the result, the effective refractive index (n~ff) has a determined negative slope to the changes in the voltage applied and changes linearly. Thatistosay,theeffectiverefractiveindexdecreases depending upon an application of voltage and the Bragg wavelength shifts to the side of short wavelength.
And, in such the planar waveguide as described above, the changes in the Bragg wavelength (A A3) to electric field (lV/
~m) is approximately 0.01 nm.
As described above, there is a linear relationship between the applied voltage and the effective refractive index and it is understood that the Pockels effect (the primary electrooptical effect) on the basis of the secondary optical nonlinearity is obtained.
It is, therefore, possible to switch light of a specific wavelength by shifting the Bragg wavelength by an application of voltage to control the transmission and non-transmission of laser light. Particularly, the planar waveguide of the present working embodiment is made of glass. Therefore, the connection with conventional optical fiber may be easily carried out. That is to say, theconnection by adhesive, laser fusing, melt-connection and the like can be easily carried out. Further, the transmittance of light at the element may be sufficiently maintained and mode mismatch is prevented .
Stillfurther, theBraggwavelength maybeshiftedinmultiple stepsby successivelychanging voltage applied. Thereby, thismay be also utilized as a wavelength selection element by controlling the transmitted wavelength.
Furthermore, in the present embodiment, the spacings of the grating may be easily controlled by the phase mask. Therefore, the grating element having desired Bragg wavelength may be easily obtained.
[ ANOTHER STRUCTURE ]
The planar waveguide of the present invention may be utilized in a variety of functional elements. For example, it may be preferable as shown in Fig. 5 to design a structure where the core area 14 is once divided to two branches which rejoin each other, and the electrodes 12a and 12b are placed respectively to the branched portions so as to apply voltage.
With such a structure, it is possible to control the phases of two branched two light rays by controlling the voltage applied tothetwobranchedportions, andit isthereforepossibletoeffect the attenuation of output light by shifting the phases of both 180 degree and optical strength modulation.
Arrangementofelectrodesisnotrestrictedtothearrangement shown in Fig.5,and electrodes 12c and 12d may also be placed on the core area 14 as shown in Fig.6. In this case, the electrodes 12cand 12dmay bepreferablyformed afterremovaloftheelectrodes 12a and 12b which have been used at the time of ultraviolet light poling. With such the structure, modulation similar to that described above may be effected.
According to the planar waveguide of the present invention, portions having optical nonlinearity may be formed on any desired area of the glass substrate 10. Therefore, various kinds of optical functional elements and optical functional circuits may be formed.
For example, a signal generator, an optical switch/coupler, or the like for the two-way optical transmission system shown in Fig.7 may be configured using the planar waveguide of the present invention. Thatistosay,twoterminalslOOareshowninthesystem illustrated in Fig.7 (there are a number of terminals 100 in conventional systems). These terminals 100 are connected with optical fiber 102 via a transducer 104. The transducer 104 controls the connection of desired optical fiber 102.
Each terminal 100 comprises a light source lOOa, a signal generator lOOb, an optical switch/coupler, and a light receiving element lOOd. The light source lOOa is a laser source generating a specific light,andthesignalgeneratorlOObopticallymodulates that light to include the information to be transmitted. The optical switch/coupler lOOc transmits the optical signals generated from the signal generator lOOb to the transmission optical fiber 102 at the time of transmission and supplies the optical signals generated from the transmission optical fiber 102 to the light receiving element lOOd at the time of receiving. The light receiving element lOOd transduces input optical signals to electric signals. The information transmitted may be demodulated by modulating the electric signals obtained by the light receiving element lOOd. An optical connector 106 connects the terminal 100 with the transmission optical fiber 102.
As described above, a transmission system making use of opticalfibermaybemadeup,andtheplanarwaveguideofthepresent inventionmaybepreferablyutilizedwiththesignalgeneratorlOOb, the optical switch/coupler lOOc, or the like.
[INDUSTRIAL APPLICABILITY]
The present invention may be utilized for an optical 16 functional element such as an optical signal generator, an optical switch/coupler, or any similar element in an optical fiber transmission system.
.. . . . ..
Claims (4)
1. A process for producing a planar waveguide characterized in that a pair of electrodes made of a conducting material are arranged on the surface of a glass substrate at a gap corresponding to a core area of the waveguide, and the surface of the glass substrate is irradiated with ultraviolet light through said gap in a state where voltage is applied between the electrodes to apply ultraviolet excitation poling to said core area.
2. A process for producing a planar waveguide comprising;
a step of forming a conducting metal film on the surface of a glass substrate, a step of etching the metal film thus formed to form a pair of electrodes spaced at determined gap, a step of injecting specified atoms on the surface of the substrate under said gap using the electrodes formed as masks to form a core area, and a step for irradiating the core area with ultraviolet light while voltage is applied between said pair of electrodes to effect ultraviolet excitation poling and impart optical nonlinearity to the core area.
a step of forming a conducting metal film on the surface of a glass substrate, a step of etching the metal film thus formed to form a pair of electrodes spaced at determined gap, a step of injecting specified atoms on the surface of the substrate under said gap using the electrodes formed as masks to form a core area, and a step for irradiating the core area with ultraviolet light while voltage is applied between said pair of electrodes to effect ultraviolet excitation poling and impart optical nonlinearity to the core area.
3. A process for producing a planar waveguide described in claim 2, wherein the irradiation of said core area with ultraviolet light is effected through a specific phase mask to form periodic regions having optical nonlinearity in the core area.
4. A planar waveguide comprising;
a glass-made substrate, a pair of electrodes formed on the substrate via a determined gap, and a core area formed on the surface of the substrate under the gap between the pair of electrodes, the refractive index of which is different from that of the substrate due to addition of specified atoms, and said core area being given optical nonlinearity of 1pm/V or above as electrooptical coefficient.
a glass-made substrate, a pair of electrodes formed on the substrate via a determined gap, and a core area formed on the surface of the substrate under the gap between the pair of electrodes, the refractive index of which is different from that of the substrate due to addition of specified atoms, and said core area being given optical nonlinearity of 1pm/V or above as electrooptical coefficient.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8/244965 | 1996-09-17 | ||
| JP8244965A JPH1090546A (en) | 1996-09-17 | 1996-09-17 | Production of plane waveguide and plane waveguide |
| PCT/JP1997/003186 WO1998012592A1 (en) | 1996-09-17 | 1997-09-10 | Manufacture of planar waveguide and planar waveguide |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2266682A1 CA2266682A1 (en) | 1998-03-26 |
| CA2266682C true CA2266682C (en) | 2002-11-12 |
Family
ID=17126594
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002266682A Expired - Fee Related CA2266682C (en) | 1996-09-17 | 1997-09-10 | Manufacture of planar waveguide and planar waveguide |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US6374026B1 (en) |
| EP (1) | EP0927906A4 (en) |
| JP (1) | JPH1090546A (en) |
| KR (1) | KR20000036168A (en) |
| AU (1) | AU716343B2 (en) |
| CA (1) | CA2266682C (en) |
| WO (1) | WO1998012592A1 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1999046632A1 (en) * | 1998-03-12 | 1999-09-16 | Toyota Jidosha Kabushiki Kaisha | Method of fabricating optical nonlinear thin film waveguide and optical nonlinear thin film waveguide |
| JP3852213B2 (en) * | 1998-07-30 | 2006-11-29 | トヨタ自動車株式会社 | Nonlinear optical silica material and nonlinear optical element |
| JP3533950B2 (en) * | 1998-08-07 | 2004-06-07 | トヨタ自動車株式会社 | Method for producing nonlinear optical silica thin film and nonlinear optical silica element |
| KR100441716B1 (en) | 1999-02-16 | 2004-07-23 | 도요다 지도샤 가부시끼가이샤 | Optical nonlinearity material and production method therefor |
| JP2001337302A (en) | 2000-05-26 | 2001-12-07 | Nec Corp | Optical waveguide element and method for manufacturing the same as well as optical polling method |
| WO2003003104A1 (en) * | 2001-06-29 | 2003-01-09 | Mitsubishi Denki Kabushiki Kaisha | Polarization dispersion compensating apparatus |
| JP2007298895A (en) * | 2006-05-08 | 2007-11-15 | Nec Corp | Optical element, integrated optical device, and manufacturing method therefor |
| FR2953607B1 (en) * | 2009-12-09 | 2012-05-18 | Commissariat Energie Atomique | DEVICE FOR COUPLING AN ELECTROMAGNETIC WAVE BETWEEN A WAVEGUIDE AND A SLOTTED METAL GUIDE, METHOD OF MANUFACTURING THE SAME |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2299662A1 (en) | 1974-06-14 | 1976-08-27 | Thomson Csf | ELECTRO-OPTICAL SWITCH AND METHOD OF MANUFACTURING SUCH A SWITCH |
| DE2614859A1 (en) | 1976-04-06 | 1977-10-27 | Siemens Ag | METHOD FOR MANUFACTURING LIGHT GUIDE STRUCTURES WITH INTERMEDIATE ELECTRODES |
| DE2614871C3 (en) * | 1976-04-06 | 1981-05-27 | Siemens AG, 1000 Berlin und 8000 München | Process for the production of thin-film light guide structures |
| US5239407A (en) * | 1991-09-27 | 1993-08-24 | University Of New Mexico | Method and apparatus for creating large second-order nonlinearities in fused silica |
| US5478371A (en) | 1992-05-05 | 1995-12-26 | At&T Corp. | Method for producing photoinduced bragg gratings by irradiating a hydrogenated glass body in a heated state |
| US5287427A (en) | 1992-05-05 | 1994-02-15 | At&T Bell Laboratories | Method of making an article comprising an optical component, and article comprising the component |
| US5235659A (en) | 1992-05-05 | 1993-08-10 | At&T Bell Laboratories | Method of making an article comprising an optical waveguide |
| AUPM956694A0 (en) | 1994-11-18 | 1994-12-15 | University Of Sydney, The | Inducing or enhancing electro-optic properties in optically transmissive material |
| US5617499A (en) * | 1995-09-08 | 1997-04-01 | University Of New Mexico | Technique for fabrication of a poled electrooptic fiber segment |
| KR100288742B1 (en) * | 1997-03-12 | 2001-05-02 | 윤종용 | Fabrication method for optical waveguide |
| EP0872756A1 (en) * | 1997-04-14 | 1998-10-21 | BRITISH TELECOMMUNICATIONS public limited company | Optical modulator |
-
1996
- 1996-09-17 JP JP8244965A patent/JPH1090546A/en active Pending
-
1997
- 1997-09-10 EP EP97940329A patent/EP0927906A4/en not_active Withdrawn
- 1997-09-10 KR KR1019997002220A patent/KR20000036168A/en not_active Application Discontinuation
- 1997-09-10 CA CA002266682A patent/CA2266682C/en not_active Expired - Fee Related
- 1997-09-10 US US09/254,672 patent/US6374026B1/en not_active Expired - Fee Related
- 1997-09-10 AU AU42190/97A patent/AU716343B2/en not_active Ceased
- 1997-09-10 WO PCT/JP1997/003186 patent/WO1998012592A1/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| EP0927906A1 (en) | 1999-07-07 |
| JPH1090546A (en) | 1998-04-10 |
| EP0927906A4 (en) | 2002-10-02 |
| AU716343B2 (en) | 2000-02-24 |
| AU4219097A (en) | 1998-04-14 |
| US6374026B1 (en) | 2002-04-16 |
| WO1998012592A1 (en) | 1998-03-26 |
| CA2266682A1 (en) | 1998-03-26 |
| KR20000036168A (en) | 2000-06-26 |
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